Solutions colligative properties of electrolyte

A family uses a commercially available desalinator, similar to those developed by the Navy for life rafts. The essential part of these desalinators is a cellophane-like membrane wrapped around a tube with holes in it. Seawater is forced through the tube by a hand-operated pump at pressures of about 70 atm to produce water with a salt content only 40% higher than that from a typical tap. 

Salt water is forced through 20-micron and 5-micron filters at a pressure of 800 pounds per square inch. 

Fresh water is forced through additional filters. 

Fresh water is pumped into water supply. 

Residents of Catalina Island off the coast of southern California are benefiting from a desalination plant that can supply 132,000 gallons of drinkable water per day, one-third of the island s daily needs. 

As we have seen, the colligative properties of solutions depend on the total concentration of solute particles. For example, a 0.10 m glucose solution shows a freezing-point depression of 0.186°C  

On the other hand, a 0.10 m sodium chloride solution should show a freezing-point depression of 0.37°C, since the solution is 0.10 m Na+ ions and 0.10 m Cl- ions. Therefore, because the solution is 0.20 m in solute particles, AT = (1.86°C kg/mol)(0.20 mol/kg) = 0.37°C. 

The relationship between the moles of solute dissolved and the moles of Dutch chemist J. H. van t Hoff particles in solution is usually expressed by the van t Hoff factor (i)  

In an aqueous solution a few ions aggregate, forming ion pairs that behave as a unit 

TABLE 17.6 Expected and Observed Values of the van t Hoff Factor for 0.05 m Solutions of Several Electrolytes 

Salt water pumped from underground wells. 

Catalina Island s plant may be just the beginning. The city of Santa Barbara opened a 40 million desalination plant in 1992 that can produce 8 million gallons of drinking water per day. The southern California city of Carlsbad opened a reverse osmosis desalination plant in 2012 that can produce 50 million gallons of drinking water daily from seawater. Desalination plants are also in the woiks for Huntington Beach, California, and Camp Pendleton, a military base just north of Carlsbad. 

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The colligative properties of electrolyte solutions are described by including the van t Hoff factor in the appropriate equation. For example, for changes in freezing and boiling points the modified equation is... 

COLLIGATIVE PROPERTIES OF ELECTROLYTE SOLUTIONS Review Questions... 

Why is the discussion of the colligative properties of electrolyte solutions more involved than that of nonelectrolyte solutions ... 

Describe electrolyte behavior and the four colligative properties, explain the difference between phase diagrams for a solution and a pure solvent, explain vapor-pressure lowering for nonvolatile and volatile nonelectrolytes, and discuss the van t Hoff factor for colligative properties of electrolyte solutions ( 13.5) (SPs 13.6-13.9) (EPs 13.59-13.83)... 

A U. luO-L solution is made by dissolving u.44i gof CaCl2(s) in water, (a) Calculate the osmotic pressure of this solution at 27 "C, assuming that it is completely dissociated into its component ions, (b) The measured osmotic pressure of this solution is 2.56 atm at 27 C. Explain why it is less than the value calculated in (a), and calculate the van t Hoff factor, i, for the solute in this solution. (See the A Closer Look box on Colligative Properties of Electrolyte Solutions in Section 13.5.) (c) The enthalpy of solution for CaCl2 is AH = —81.3 kj/mol. If the final temperature of the solution is 27 °C, what was its initial temperature (Assume that the density of the solution is 1.00 g/mL, that its specific heat is 4.18 J/g-K, and that the solution loses no heat to its surroundings.)... 

Colligative Properties of Electrolyte Solutions 540 Using Spectroscopic Methods to Measure Reaction Rates 564 Limitations of Solubility Products 726 Other Greenhouse Gases 764... 

Colligative properties of electrolyte solutions depend on the number of particles produced during the ionization or dissociation of the electrolyte. 

When solute and solvent are volatile, each lowers the vapor pressure of the other, with the vapor pressure of the more volatile component greater. When the vapor is condensed, the new solution is richer in that component than the original solution. Calculating colligative properties of electrolyte solutions requires a factor (/) that adjusts for the number of ions per formula unit. These solutions exhibit nonideal behavior because charge attractions effectively reduce the concentration of ions. 

Except in very dilute solutions, the values of colligative properties of electrolyte solutions are less than expected because of the attraction between ions in solution. 

For example, when 1 mol of NaCl dissolves in water, it forms 1 mol of dissolved Na" ions and 1 mol of dissolved CF ions. Therefore, the resulting solution has 2 mol of dissolved particles. The colligative properties of electrolyte solutions reflect this higher concentration of dissolved particles. In this section we examine colligative properties of nonelectrolyte solutions we then expand the concept to include electrolyte solutions in Section 12.7. 

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